Can't calibrate for impedance measurements

[wus]

I want to use REW to make impedance measurements. Help (REW v5.20) says to first calibrate the setup, starting with an open circuit measurement which should show a difference reading in percent. However I don't get this, what I get instead is this:

I nevertheless tried to proceed with the short circuit calibration as described in the help, but can't activate the short circuit cal button in the impedance measurement dialog. The open circuit cal button is still red. Help says "the button text is red if impedance calibration has not been done", so apparently REW doesn't recognize my previous measurement as the first calibration step.

What's going wrong here?

 

[John Mulcahy]

When you do the open circuit measurement the measurement input and the ref input should have the same signal level, since there should be no load on the measurement input and the ref is looped back from the measurement output before the sense resistor. In that cal run the measured was just 27 % of the ref (for the open circuit cal the impedance value shown is the relative gain in percent). Such a large difference shouldn't happen and won't be accepted. If you have independent gain controls for the two input channels they may be set differently, they should be set to the same gain. Otherwise something may be wrong with your setup.